They cut a stylish swath through Capitol Hill: a distinguished Brit, a dapper Frenchman with colorful pocket squares and a floppy-haired German in black-framed glasses.

As the Obama administration steps up its campaign to sell the Iran nuclear deal on Capitol Hill, it is welcoming the assistance of Europe’s top ambassadors to Washington.

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Obama administration officials flooding Congress to sell the pact are now working in tandem with ambassadors from the three European nations — Great Britain, France and Germany — that also signed off on the July 14 agreement.

The diplomatic trio, whose countries are known together as the “E3,” echo administration talking points and parries specific concerns from skeptical members of Congress. They also push a signature message: that the Iran deal is an international agreement, not just the handiwork of a Democratic president scorned by the GOP.

“We think it’s important that people who will vote on the bill understand that it’s not just about this administration and the Iranian government. The other governments who are part of the deal, what we call the P5+1, also have views on it and also think it’s the right way to go,” British Ambassador Peter Westmacott told POLITICO just after meeting with senators on Tuesday.

The term P5+1 describes the five permanent members of the U.N. Security Council — Britain, France, Russia, China, the United States — plus Germany. Also canvassing the Hill is the European Union’s ambassador to Washington, David O’Sullivan.

European officials hope that by reminding members of Congress about support for the deal from British Prime Minister David Cameron, German Chancellor Angela Merkel and French President Francois Hollande, they can defuse any partisan impulse to oppose President Barack Obama’s signature foreign policy achievement.

“Especially when it comes to addressing Republican members of Congress, it is good to add in the E3 perspective because it might not be regarded as biased, or as much like a partisan issue,” said Markus Knauf, a spokesman for the German Embassy in Washington.

To that end, Berlin’s ambassador, Peter Wittig, recently hosted several Republican House members for a dinner at his chic residence with a scenic view of Washington’s leafy Palisades neighborhood. The guest list included Reps. Erik Paulsen, Charles Boustany, Martha McSally and Elise Stefanik.

Westmacott, Wittig and France’s ambassador to Washington, Gérard Araud, met together last week with Bob Corker, chairman of the Senate Foreign Relations Committee, for what Araud later tweeted was a “courteous exchange of views.”

Westmacott estimated that he has met or spoken with at least two dozen members of the House and Senate about the deal this month. “It’s been a quite a big part of my life,” he said over coffee in the basement of the Senate’s Dirksen office building.

Sources said that diplomats from Moscow and Beijing, which have testier relations with the U.S., have not played a visible role in promoting the deal.

The Europeans are working in competition with Israeli ambassador Ron Dermer, who has also visited numerous members of the House and Senate, telling them that the administration is exaggerating the consequences of opposing the deal.

Under a measure passed by Congress in March, the House and Senate can vote to approve or disapprove the nuclear agreement, which imposes long-term limits on Iran’s nuclear program in return for an end to sanctions on Tehran. If Congress votes to oppose the deal and continue U.S. sanctions, Obama is sure to veto the measure. A two-thirds majority in both the House and Senate is required to override a White House veto.

Obama administration officials express cautious optimism about their ability to defend the deal, while opponents insist they have a real chance of derailing it. An initial vote is expected by mid-September.

The Europeans are coordinating closely with the State Department and working from a communications game plan their foreign ministers shaped, along with Secretary of State John Kerry, as the nuclear talks concluded in Vienna earlier this month.

Their talking points parallel those of Obama and Kerry, particularly the argument that there is no realistic alternative to the nuclear deal other than a dangerous confrontation with Iran.

“The fundamental point that I keep trying to make to people is that this is an agreement that has been negotiated and agreed by the six governments, and we do not judge that there is a better alternative out there for stopping Iran’s development of nuclear weapons,” Westmacott said.

“If you kill this deal, what is the alternative?” he asked. “I find that the response to that question is deeply unsatisfying, because all the alternatives, in my judgment, are worse.”

Though it would be undiplomatic for the European envoys to criticize American politics, they do note that their home countries lack the roiling debate around the Iran deal that is now consuming Washington.

“There’s a very interesting contrast between the politics in the other P5+1 capitals” and in Washington, Westmacott said. “In the others this is not a matter of political controversy. This is not a partisan issue.”

In German politics, Knauf added, “only fringe people see this as not a good deal.”

Araud is the bluntest of the bunch, particularly on his notoriously colorful Twitter account.

“When Americans use the cliche of Munich,” he tweeted on July 21, “I feel like reminding them the US was nowhere to be seen when France and UK were facing Hitler.”

It’s not clear what impact the European lobbying might have, particularly among Republicans who often deride European views of international security. France and Germany infuriated the GOP by opposing the Iraq War in 2003. More recently, however, France has grown more hawkish, and at times took a harder line on the nuclear talks than the Obama administration.

Supporters of the deal have also enlisted some less traditional messengers. On Tuesday, the group Global Zero, a nonprofit working to eliminate nuclear weapons, released a three-minute satirical video featuring the actors Jack Black and Morgan Freeman and Jordan’s Queen Noor making a case for the nuclear deal and warning that the alternative could be “war with Iran.”

“It would be like a really dark unpleasant cloud of death,” Black warns in the video, before concluding: “Playing politics with our national security is actually not all that funny.”